Nice routes around South London are hard to come across, and this is the nearest route to me that I have found to get out onto a good road or two.
The loop indicated is quite nice and easy to get to from South London, although it is not very long. You can stop off at a cute little town called Westerham for a drink/afternoon tea, and from there you are on the A25, so can easily go to Boxhill (West) or Oakdene Cafe (East, near Brands Hatch), or head off South from here onto one of the many nice roads into Kent/Sussex.
Dartford, Darenth, Longfield, Meopham, Wrotham, Addington, Wateringbury, West Farleigh, Coxheath, Chart Sutton, Sutton Valance, Headcorn, Tenterden, Wittersham, Playden, Rye
A nice Sunday morning ride and when you get to Rye pop down to Camber Sands for a cup of tea and get ready for zapping across Romney Marshes. Or go for a ride on the Romney marshe and Dymchurch miniture railway.